Compression ignition engines have been in use for many years and are popularly known as "diesel" engines. In such engines, ignition occurs due to the compression energy and high pressure injection of fuel in the engine. Starting such engines is much easier when additional heat is provided to aid in igniting the fuel. Such additional heat may be supplied by increased combustion air temperature and/or the use of a device known as a glow plug which is essentially a resistance heating element placed in the combustion chamber of the engine.
Such arrangements have worked reasonably satisfactorily. However, and with the advent of alternative fuels and with the desire to introduce less contaminants into the atmosphere, it is desirable to provide such additional heat not only during initial engine startup but during the operation of the engine. The additional heat is particularly advantageous when supplied during startup of the engine and during the application of loads to the engine.
Some ignition systems have been proposed in the past for controlling the provision of additional heat during the combustion process until the engine reaches a certain temperature. Such systems have generally relied on sensing coolant temperature or the like. While these systems will operate, it should be understood that a substantial time delay occurs between changes in the temperature of the engine coolants and the events occurring in the engine combustion chamber. Also, ignition systems have been proposed which utilize special glow plugs and are thus not entirely satisfactory for retrofit on existing engines.
An object of this invention is to provide an improved fuel ignition system for compression-ignited engines that utilizes standard glow plugs for generating a signal to indicate the combustion chamber temperature and that accordingly can be retrofitted onto existing engines as well as manufactured into new engines.